1. Field of the Invention
The present invention relates to electromagnetic exciters that may be incorporated into mobile communications devices such as cellular phones and personal digital assistants (PDAs) to inform the user of an incoming call by vibrating a panel or a housing of a phone, for example.
2. Description of the Background Art
Conventionally, mobile communications devices such as cellular phones and personal digital assistants are arranged to inform the user of an incoming call by selectively generating beep sound or melody sound, or vibrating the housing of the device instead of producing sound. For this purpose, these communications devices incorporate a combination of a speaker for generating sound and a vibration-generating device that generates vibration by rotating an eccentric weight with a small motor. Incorporating both a speaker and a vibration-generating device into such a communications device, however, is disadvantageous from the viewpoint of achieving size and cost reduction of the device. Under these circumstances, use has recently been made of an electromagnetic exciter that can selectively generate sound and vibration.
The present applicant filed an application for a patent on an electromagnetic exciter (Japanese Patent Laid-Open Application Publication No. 2006-333273). The electromagnetic exciter in this previous application has, as shown in FIG. 4, a magnetic circuit assembly 21 including a cup-shaped yoke 22, a combination of a plate-shaped magnet 23 and a top plate 24 that are successively stacked in the yoke 22, a voice coil 25 that is inserted into a magnetic gap g formed between the inner peripheral portion of the yoke 22 and the outer peripheral portion of the top plate 24 and a weight 29 that is secured to the outer peripheral surface of the yoke 22.
The magnetic circuit assembly 21 is, as shown in FIGS. 4 and 5, supported by a cylindrical suspension 26 formed by deep drawing a metal sheet in a press. More specifically, the suspension 26 has a cylindrical side wall portion 26a, a ring portion 26b formed along the bottom edge of the cylindrical side wall portion 26a, a dish-shaped portion 26c located radially inside the ring portion 26b, and a pair of arcuate spring portions 26d connecting the ring portion 26b and the dish-shaped portion 26c. The dish-shaped portion 26c is fixed to the magnetic circuit assembly 21 by laser welding or the like. The suspension 26 suspends the magnetic circuit assembly 21 vibratably in the vertical direction as seen in FIG. 4.
An annular support member 27 is fitted and secured in the upper end opening of the cylindrical side wall portion 26a of the suspension 26. A printed wiring board 28 is fixed to the annular support member 27. The printed wiring board 28 supports the voice coil 25 and is provided with wiring patterns electrically connected to the ends of the voice coil 25 and enabling electrical connection to an external device in which an electromagnetic exciter is placed.
The electromagnetic exciter is installed by fixing the printed wiring board 28 to the housing of an electronic device such as a cellular phone. When the voice coil 25 is excited by a driving signal input thereto, the voice coil 25 and the magnetic circuit assembly 21 vibrate relative to each other by interaction therebetween. When the driving signal is of a relatively high frequency in an audio-frequency region, the voice coil 25 mainly vibrates, causing the housing of the electronic device to vibrate through the printed wiring board 28. When the frequency of the driving signal is low, the magnetic circuit assembly 21 mainly vibrates, causing the housing of the electronic device to vibrate through the suspension 26.
FIGS. 6 and 7 show an improvement on the above-described electromagnetic exciter. The illustrated electromagnetic exciter is substantially the same as the above in regard to the main structure. The improved electromagnetic exciter is additionally provided with a second suspension 31 that supports the upper end portion of the magnetic circuit assembly 21. The second suspension 31 has an outer ring portion 31a, an inner ring portion 31b, and arcuate spring portions 31c, which respectively correspond to the ring portion 26b, the dish-shaped portion 26c and the arcuate spring portions 26d of the above-described suspension 26 (hereinafter referred to as “first suspension 26”). The outer ring portion 31a is secured to the annular support member 27, and the inner ring portion 31b is fixed to the upper end surface of the yoke 2, whereby the magnetic circuit assembly 21 is suspended vibratably in the vertical direction. In this electromagnetic exciter, the bottom (ring portion) 26b and side wall portion 26a of the first suspension 26 are partly covered with a protector 30.
In the electromagnetic exciter having the above-described structure, if an impact is applied thereto, for example, due to a fall, the magnetic circuit assembly may be shifted so much that the top plate collides with the printed wiring board. This may result in separation between the printed wiring board and the frame (i.e. the cylindrical side wall portion of the first suspension)